Many electronic applications operate on multiple power sources. In other words, these applications may operate on one power source in one mode of operation, and then on a different power source in another mode of operation. One example is a personal computer (PC) system. A PC system specifies multiple power sources, or operating voltages, at 12 volts (V), 5 V and 3.3 V for various operations. For instance, the output voltage of a computer system in an idle mode is different from that of the computer system in a fully operational mode.
Another example of a system that operates on multiple power sources is a wireless communications system. In a local area network (LAN), data packets may be transmitted using different technologies. The most widely used LAN technology is the Ethernet. Ethernet has many varieties in speed and physical medium used. The modes of operation in popular commercial application are the 10 Base-T, 100 Base-TX and 1,000 Base-T, run at 10 Mbps, 100 Mbps and 1 Gbps, respectively. Because these modes operate at different voltage levels, a product that supports all three modes of operation must include a driver that is capable of operating and providing at different voltage levels. There are two basic architectural options for the Ethernet drivers: current source or voltage source. Typically, the current source is used for 10Base-T mode of operation and the voltage source is used for 100Base-TX mode of operation. In a multi-mode Ethernet network, therefore, different operating voltages often cause significant power consumption.
Conventional systems provide either a current source or a voltage source during any given mode of operation, believing using only one power source at a time will save power. Specifically, in a 10BaseT mode, only a current source is used and the voltage source is turned off or placed in standby mode wherein no current is output to drive the system. In the 100BaseT mode, only the voltage source is used, and the current source is turned off or placed in standby mode wherein no voltage is output to drive the system. This type of alternating the power source necessarily requires added voltage and current requirements for each mode of operation.